Electromechanical transducer



Dec. 8, 1959 R c. FlNVOLD ELECTROMECHANICAL TRANSDUCER 2 Sheets-Sheet 1 Filed Au 20, 1956 mm mm mm bon i Tut nllQFu. L

' INVENTOR. RODGER FINVOLD ATTORNEY Dec. 8, 1959 R. c. FINVOLD ELECTROMECHANICAL TRANSDUCER Z'Sheets-Sheet 2 Filed Aug. 20, 1956 E I- B A T N 4 9 M. n

INVENTOR.

AMPLIFIER LpDlFFERENTlAL DIFFERENTIAL AMFRLITIER 0.

INPUT sIGNAIL {\TTORNEY United State ELECTROMECHANICAL TRANSDUCER Rodger C. Finvold, San Diego, Calif., assignor to General Dynamics Corporation, San Diego, Calif a corporation of Delaware Application August 29, 1956, Serial No. 605,125

3 Claims. 01. 121-41 This invention relates to valves and more particularly to electrical actuation or control of hydraulic or pneumatic valves.

Hydraulic servo systems offer considerably faster dynamic response than electric or pneumatic systems. With recent advances in hydraulic techniques and equipment, hydraulic servos with larger capacities and faster responses have been developed. The electrohydraulic valve is a necessary part in providing the adequacy and reliability of hydraulic control systems. Its basic function is control of a large output power delivered to the hydraulic actuator with a low power electrical signal. In some respects the valve may be compared to an electronic power amplifier. Electrohydraulic valves heretofore have been used in which an electrical input signal was required by the transducer for valve actuation. These valves consist of three basic sections, the electrical trans ducer section, the hydraulic pre-amplifier section, and the hydraulic output section which is then connected to the actuator, such as a piston or hydraulic motor. The electrical transducer section consisted of a torgue motor, a solenoid, or piezoelectric crystals which transferred the electrical input signal into a physical movement. This physical movement was then amplified at the hydraulic pre-amplifier section, through the use of nozzle flappers, jet pipes, flat plates or spools, and this amplified physical movement in turn actuated the hydraulic output stage which might be a four-way spool, a hole and plug, or a fiat plate. The hydraulic output stage thus controlled the fluid flow or pressure which comes from the pressure supply tank to the actuator. In some instances the hydraulic pro-amplifier section is not necessary. The actuator in turn may be either a piston connected to the object to be moved or a rotary hydraulic motor which rotates an output shaft.

The torque motor type transducer provides only a small angular displacement with a resulting short stroke. This requires the fabrication of very accurate spools, if such were used in the hydraulic pro-amplifier stage and the torque is proportional to the current magnitude of the input only over a restricted range. The solenoid type electrical transducer had poor dynamic response and the load driven by the armature has to be kept to a minimum. The solenoid also introduces hysteresis problems which produces a leaky flow for a zero input current as the current is cycled from zero over its entire range and back to zero. Usually solenoids are used in pairs, arranged for push-pull activation of the valve.

In the electrohydraulic valve comprising the present invention a transducer responsive to input signals is used for driving the pilot spool in the hydraulic preamplifier stage. The output stage spool is so arranged relative to the pilot spool that a minimum of fluid movement is necessary to move the output spool in tracking relation to the movement of the pilot spool. The output spool then opens suitable ports so that the fluid from the supply tank under pressurewill operate the actuator, which in turn moves the table or other object to be moved. A dynamoelectric transducer pickup is provided for producing an electrical signal output responsive to movement of the pilot spool, output spool, or the actuator, as desired, to check the relationship between the input signal to the transducer and the response of the different parts in the hydraulic system. Means are provided for rotating the pilot spool and transducer to overcome static friction. Slip rings are provided for the energization of the input transducer and to provide an output from the pickup. This output may be used in suitable feedback circuitry to correct any error in the valve system or to energize indicating instruments. The advantages of this device over those now in use are that it has a higher frequency response up to several times that of present type valves, that its response is linear from the input to the transducer to the output force developed for mass actuation, and that it does not have error due to hysteresis efl'ects normally found in torque motor and solenoid transducers. Thcvalve can accept random signal pulses as well as sinusoidal signals, which solenoid drivers could not faithfully reproduce due to limited frequency response. The movement of the spools, which is proportional to the signal, is proportional over the full travel of the spool and therefore provides linearity in the device.

Piezoelectric transducers require a relatively large electrical input and because of limited physical movement, require amplification before valve actuation. By providing the two spools in concentric arrangement, less fluid is necessary to drive the output spool in tracking the pilot spool. The factor of fluid compressibility becomes less important and also a more compact device is possible.

It is therefore an object of this invention to provide for an improved electrohydraulic valve.

Another object is the provision of an electrohydraulic servo valve having an electrodynamic transducer responsive to input electrical signals.

Another object is the provision of an electrohydraulic valve responsive to input random electrical signals as well as sinusoidal input signals and wherein the valve may be placed in a position remote from the object being actuated.

Another object is the provision of an electrohydraulic servo valve having a linearity of response between the input to the transducer and the output fluid flow to the actuator.

A further object of this invention is the provision of an clectrohydraulic valve having a linear response to signals of high frequency (in the order of 2000 cycles per second).

Still another object is the provision of a novel actuation and feedback means for use in an improved electrohydraulic servo control valve.

Still another object is the provision of a novel electrohydraulic valve actuated table arranged for movement about at least one axis in response to electrical signals energizing the valve.

Still another object is the provision of an hydroelectric servo valve wherein the spool position determines fluid and actuator velocity and wherein spool position is determined by the input electrical signal.

Still another object is the provision of an electrohydraulic servo valve having a spool velocity which produces an actuator acceleration proportional to the input signal.

Still another object is the provision of an electrohydraulic servo valve including a spool having a selected mass whereby the acceleration of the spool is proportional to the input electrical signal.

A further object is the provision of a valve which is relatively easy and inexpensive to fabricate, dependable in operation and requires a minimum of maintenance.

Qther objects and features of the present invention ment.

will be readily apparent to those skilled in the art from the following specification and appended drawings wherein is illustrated a preferred form of the invention, and in which: Figure l is a cross-sectional view of the moving coil valve actuating system and feedback pickup coil;

Figure 2 shows the moving coil driving a single stage control section reacting against a spring element with the pickup attached to the same end of the same shaft; Figure 3 shows a moving coil driver and valve for actuating a table in a predetermined path with a dynamoelectric actuator sensing device for feedback or indicating purposes; and V Figure 4'shows a preferred valve feedback loop using both pickup and driving moving coils.

Depending upon their desired use, electrohydraulic valves are designed according to three modes of operation as defined by the formula F=Ma+Rv+Sx,

where. F=force, M=rnass, a=acceleration,' R=resistance, i -velocity, S=spring constant and x=displace- If valve acceleration is the desired feature, the value of M is made much larger than R or S so that the values of Rv and Sx in the formula are relatively small and insignificant. If valve velocity isconsidered important, its resistive forces R are made large and M and S small. For valve position, a spring with a large spring constant S is used. This method of mode selection (the open loop) is by physical design in which theirelative magnitudes of M, R and S determine the valves functional use. The closed loop method of accomplishing the desired mode ofoperation is done with dynamoelectric transducers providing feedback signals back into a difierential amplifier to provide a velocity v, acceleration a, or position x, proportional to the input signal. The feed-back transducers may be moving coil pickup, accelerometer, strain gage, a potentiometer, depending upon the desired mode of' operation. a

The moving coil valve operating transducer, comprising the present invention, may be used in all three modes of valve operation. The moving coil pickup may be used except for the position finding mode. The valve in Fig. 1 has two stages, preamplifier and power output, and the valve in Fig. 2 has only one. One valve initiates fluid flow while. the other is used in a free circulating fluid system. The valve in Fig. 1 has no measurable spring constant (actually no spring is used and the Bernoulli spring effect has been overcome) and is used where valve velocity or acceleration is desired. The valve in Fig. 2 has a large spring restraint for positioning the spool, and'regulating fluid velocity, proportional to the input signal. In addition, the moving coil pickup positioned at selected points in the valve or actuating system is used to sense theresponse for indicating purposes or for use in either or both of the feedback systems shown in Fig. 4.

Referring now to Fig. 1, there is shown the pilot valve spool driven electrodynamically by a moving coil and field magnet resembling'a loud speaker system. The field windings 10 are wound about the center core of an E- shaped-in-cross-section iron core 11 to form an electromagnetic field. Around the end of the center core is a moving coil carrier 12 about which is mounted the moving coil windings 13. Connected to this carrier is a shaft 1 4 connected to a pilot spool '16, all adapted for rotation as well as axial movement. The shaft 14 is rotated by an electric motor pulley and belt drive assembly 15. Connected to the moving coil 13 and mounted on the shaft14 are slip rings 21 through which is fed the inputsignal to the moving coils 13 which moves the shaft 14 back and forth in response to the signals. A

concentric power output stage spool 17 which controls the fluid flow .to the actuator 18 (shown in Fig. 4) is hydraulically driven to follow up the position of the pilot spool 16 in a master-slave relationship. Extending from the valve housing 23 is a shaft 24 to which is connected a second moving coil carrier 26 about which is wound the moving coil windings 27. These windings move back and forth in response to axial shaft movement of output spool 17. In the presence of a magnetic field generated by windings 28 about a core 29 they induce an electrical signal to output terminal 32. Shaft 24 also may be connected to the pilot spool 16 as shown in Fig. 2 to provide an electrical output responsive to its movement. This output may be used for a feedback arrangement as will bepointed'out with reference to Fig. 4 or it may be used in some indicating device for translating spool position, velocity or acceleration into terms of force applied to the table or other object actuated.

The valve shown in Fig. 1 operates as follows: In the presence of a magnetic field induced by windings 10 about core 11, any random or sinusoidal signal induced in windings 13) through slip rings 21 causes carrier 12 to move shaft 14 in an axial'direction. Signals of one polarity move the shaft in one direction and signals of the opposite polarity move it in the opposite direction. The amount of' movement depends upon the strength of the signal. Assumeshaft 14 moves pilot spool 16 to the right. Fluid from the pressure tank connected to pressure port 33 enters orifice '34. From there the fluid exerts pressure in opening 3'5 to the left of power spool 17, moving it also to the right in master-slave relationship with pilot spool 16. This movement cuts off the fluid from port 33 to orifice 34 and stops the relative movement between the two spools. The movement of spool 17 to the right permits fluid flow into cylinder port 1 and thence to one side of the piston chamber to drive the piston. The fluid in the chamber on the other side of the piston must be evacuated as the piston is moved. This fluid enters cylinder port 2 and, since spool 17 is moved to the right, the fluid passes on out through drain passage 36 to drain port 37 and back to the supply tank. Now, suppose the next signal moves the pilot spool to the left. This. opens up a fluid path from chamber 115 to the drain port 37 to permit power spool 17 to also be moved to the left without fluid back resistance. With spool 16 moved to the left, fluid from port 33 passes through orifice 38 into chamber 39 to move spool 17 back into alignment with spool 16. This connects port 33 with cylinder port 2 for movement of the piston in the opposite direction. s

Figure 2 shows a single stage power output spool 41 actuated by the moving coil electromechanical transducer 42 having a spring 43 for the purpose of providing a force proportional to displacement. This spring has a high spring constant S compared to the mass M and resistance R and transforms the input signal into spool position. Spool position, in turn, regulates fluid flow and actuator velocity. Here also is shown the moving coil pickup 42 mounted to the same end of shaft 14 as the actuating transducer. This permits the use of feedback with longer spools, and at higher frequencies, which otherwise would create a' lag of greater than in the feedback system, an unstable condition causing oscillations. In general, the shorter the spool and the elfective path length from driving coil to pickup coil, the less phase shift, permitting higher frequencies of input signal without feedback problems.

Fig. 3 shows the use of the moving coil actuated electrohydraulic valve operating a table in a predetermined path. Here the pickup transducer 42 is operated by the actuator shown as a piston 18, although it might be a hydraulic motor rotating a shaft. The pickuptransducer in this position may be a potentiometer, accelerometer or moving coil used to check the response of the operating mechanism as a whole in response to the input signals. The transducer 42 may be used to show linearity or to operate an output indicating device. It may also be used in a major feedback arrangement as shown in Fig. 4 wherein the output signal from the transducer (potentiometer, accelerometer or moving coil pickup) would be fed into a differential amplifier No. 1 into which also is fed the input signal. Here the two signals are compared and the resultant is either added or subtracted from the input signal depending upon the relative amplitude and polarity of the feedback signal. Thus a greater or lesser signal might be applied to the moving coil 13 to effect an actuator response which would be linear to the input signal. A minor feedback arrangement is also shown in Fig. 4 to insure valve response linearity. Here the pickup moving coil 26 is shown responsive to movements of the valve spool (16 or 17 as desired). The pickup signal is then compared with the input signal in difierential amplifier No. 2 with the diiference or error signal correcting the valve action as necessary for linear response.

When the moving coil electrohydraulic transducer has been described in connection with the operation of spool type hydraulic pre-amplifiers and hydraulic output stages it should be obvious that its application in connection with other known types of hydraulic valves and for other purposes is well within the scope of this invention. While the use of this electrohydraulic servo valve has been shown in connection with the movement of a table, such as for shock and vibration testing purposes or to simulate flight conditions of aircraft and missiles, this valve may also be used in hydraulic-powered machine tools or other uses of hydraulic servos having large capacities and fast re sponse times, requiring adequate and reliable hydraulic control systems.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims:

What I claim is:

1. Means for controlling fluid flow in response to electric signals comprising a hydraulic valve having an internal spindle for controlling fluid flow in said valve, an electrodynamic transducer comprising means defining an annularly shaped air gap and means for producing a magnetic field in said air gap, a cylindrical member positioned within said air gap and arranged for rotational and axial movement therein, an electrical winding carried by said member, means interconnecting said member and said spindle, means for rotating said member and said spindle, and means for applying said electrical signals to said winding while said member and winding are rotating to effect axial displacement of said spindle in response to said electrical signals.

2. Apparatus for producing movement to an object in response to a signal source comprising a table supported for movement along a predetermined path and adapted to carry said object, an electrohydraulic control valve, and a hydraulic actuator responsive to fluid flow from said control valve for imparting movement to said table, said electrohydraulic control valve having an internal spindle for controlling fluid flow through said valve and including a transducer for converting an electrical signal into a force applied to said spindle, said transducer comprising means for producing a magnetic field and a coil positioned within said magnetic field and coupled to said spindle for moving said spindle in response to electrical signals applied to said coil, and moving coil converting means for translating movement of said spindle into an electrical signal, a first amplifying means having an output terminal connected with said coil for delivering electrical signals thereto, said amplifying means having two signal input terminals, one of said terminals adapted to receive electrical signals from the output of said first converting means, a second converting means responsive to table movement for translating said movement to an electrical signal, a second amplifying means, said second converting means being connected as an input to said second amplifying means, the output of said second amplifying means being connected to the other of said terminals, said second amplifying means having another in put for receiving signals from said signal source.

3. Means for controlling fluid flow in response to electric signals comprising a hydraulic valve having an inter nal spindle for controlling fluid flow in said valve, an electrodynamic transducer comprising means defining an annularly shaped air gap and means for producing a magnetic field in said air gap, a cylindrical member positioned within said air gap for rotation and axial movement therein, an electrical winding carried by said member, means interconnecting said member and said spindle, and means for applying said electrical signals to said winding during movement of said member to effect axial displacement of said spindle in response to said electrical signals.

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